This invention relates in general to respirators and in particular to a new and useful respirator including an arrangement for reducing the system pressures during exhalation by directing a pressurized gas in a circulating line connected to a breathing bag.
The invention relates to a cycle respirator for pressure operation with a compressed gas source which via a compressed gas line feeds in addition an auxiliary device which by movement of the breathing bag brings about a pressure increase in the respiratory cycle.
Such a cycle respirator is known from German OS No. 31 05 637.
In the known cycle respirator with pressure operation it is made sure that a positive pressure prevails during its use in the respiratory cycle both in the exhaling and in the inhaling phases. This positive pressure prevents during use of the apparatus the penetration of ambient atmosphere which might contaminate it and do harm to the user of the apparatus. Should leaks develop in the respiratory cycle, the created pressure makes sure that there results only a gas stream out of the respiratory cycle into the ambient atmosphere. For the user of the known respirator it means, however, an unnecessary effort that he must make, because a positive pressure is created in the respiratory cycle also during the exhalation phase. The positive pressure required for leakproofness in the sense of protection of the apparatus user is created, in fact, already in the mouthpiece or full mask by the flow resistances following them from the accordian tubes, valves and regeneration cartridges, for example. An additional static pressure burdens the apparatus user additionally and tires him prematurely,
The same is true also of the following known compressed gas respirator with positive pressure in the respiratory air according to German Pat. No. 30 15 759, which, too is designed as a cycle apparatus. Here load is applied on a breathing bag disposed in the cycle from the outside by a tensioned spring, the positive pressure being thus maintained in the cycle. From an oxygen pressure vessel the oxygen is supplied to the breathing bag via a lungmotor, which is actuated during evacuation by the movable end wall thereof. The lung-motor is preceded by a shutoff valve which, upon complete evacuation of the breathing bag, is closed by the end wall. Thereby an outflow of large amounts of oxygen is prevented in case of major leaks in the cycle or removal of the mask involving a decrease in the positive pressure.
It is, however, not possible to lower the positive pressure during the exhalation phase in the sense of relieving the apparatus user.
In another known cycle respirator according to German OS No. 31 05 637, the exhalation line is connected to the inhalation line via a CO.sub.2 absorber and a gas compensation vessel. A compressed gas bottle containing mostly oxygen communicates with the inhalation line. Best suitable as gas compensation vessel is a bellows with rigid end walls. The bellows is under the force of a cylinder piston unit, continuously acting in the sense of reducing its volume, the piston of which is connected with its end wall and admitted by compressed gas from the compressed gas bottle, expanded to a mean pressure. By the movement of the piston a lasting pressure increase is created in the bellows, sufficient for the desired positive pressure in the entire respiration cycle. By measures not shown in detail, the force acting on the bellows can be varied continuously or intermittently, whereby the pressure prevailing in the cycle can be adapted to the existing operating conditions and the respirator can be set selectively to a negative or a positive pressure operation.
As the force selected and set for the respective use acts continuously and creates a lasting pressure in the respiratory cycle via the piston, this pressure is effective both during the inhalation phase and during the exhalation phase. During exhalation, however, the user must already exert a pressure to overcome the flow resistances in the exhalation valve, lines and CO.sub.2 absorber.
By the additionally acting positive pressure he is additionally burdened unnecessarily during the exhalation in an unfavorable manner.